A wireless transfer device is known, in which a packet signal received from a wired transfer path is transmitted to an opposite station which is opposed via a wireless transfer path on a one-to-one basis and the opposite station outputs the packet signal to the wired transfer path again.
In a common technology on wireless transfer, if a multi-value number of a wireless modulation scheme is increased in the same wireless reception electric field level, wireless transfer capacity is increased and error tolerance of the wireless transfer path is deteriorated. On the contrary, if the multi-value number of the modulation scheme is decreased in the same wireless reception electric field level, the wireless transfer capacity is reduced and high error tolerance can be secured. Namely, if the multi-value number of the wireless modulation scheme is decreased in a situation in which the reception electric field level is reduced, though the wireless transfer capacity is reduced, high error tolerance can be obtained and line quality can be kept.
Generally, transmission capacity of the wireless transfer path tends to be small compared with the wired transfer path. However, since traffic is rapidly increased with recent rapid expansion of a mobile phone network and increase of data communication use, it is strongly desired to secure large transfer capacity in the wireless transfer path.
As one of techniques to secure larger transfer capacity of the wireless transfer path, an adaptive modulation function is known. When the multi-value number of the wireless modulation scheme is increased, compared with a normal operation condition, in a state in which the wireless reception electric field level is high and the line quality is high, larger transfer capacity can be acquired by using a wireless transfer device with the adaptive modulation function.
However, since the wireless transfer capacity which is used with modulation scheme changeover changes, the wireless transfer device with the adaptive modulation function needs to carry out suppression control of an amount of traffic to be sent to the wireless transfer path by following the change. If suppression control of the wireless transfer capacity and the amount of traffic is concurrently carried out when the control is carried out, traffic loss in transferring traffic and fluctuation of transfer delay time due to influence of transient buffering control, and the like, may occur.
Accordingly, in the wireless transfer device which transfers highly important traffic in which it is desirable not to generate traffic loss and fluctuation of transfer delay time, the problem is required to be solved.
Various proposals have been made, on a method for securing a reception electric field margin for maintaining a line by using the adaptive modulation function controlling the wireless modulation scheme, and for maintaining a transfer function of important traffic when the line quality of the wireless transfer path.
For example, Patent Literature 1 discloses a method for monitoring the wireless transfer capacity and controlling a signal band to be transmitted to the wireless transfer path depending on change of the wireless transfer capacity, in the system in which the transfer capacity of the wireless transfer path on the basis of the adaptive modulation control. By carrying out the method, unnecessary traffic congestion situation can be avoided and transfer rate and transfer quality of an important traffic can be maintained.